Filament-reinforced resin motor cases have been and are being extensively used in the propulsion industry. Several advantages have resulted from employment of filament-reinforced-resin motor cases. Some of the advantages include: light weight-reinforced resin motor case, the ease of manufacture, storage, transportation, and insensitivity against sparking or electrical conductance malfunctions.
Advanced interceptor motor case technology has placed additional requirements on the propulsion industry to ensure that these motor cases withstand the stresses due to the high acceleration forces resulting from employing ultrahigh burning rate propellants and kill vehicle control systems which require high maneuverability to execute difficult tactical maneuvers. It is well established that the strength of a motor case is weakened at points of stresses due to material weaknesses or inadequacies of the fabrication techniques. For filament-reinforced composite motor cases, particularly, those that include a curable resin which undergo shrinkage on polymerization, stress due to shrinkage of the resin causes an inherent defect during the manufacture of the motor case.
Laminated structures for other uses which also employ filament-reinforced resin composites are subjected to the same stress factors as a result of shrinkage on polymerization of the resin. Such shrinkage can produce defects in the fiber portion since the fibers, if subjected to excessive stress due to resin shrinkage, can undergo breakage or be weakened to below their design strength values.
A bisspiroortho carbonate, 3, 9-bis(5'-norbornene-2'-yl)-1,5,7,11-tetraoxaspiro [5.5]undecane is disclosed in applicant's U.S. Pat. No. 4,515,912, filed July 5, 1984, for use in cure shrink-resistant missile motor cases. All epoxy resin blends normally employed in filament-reinforced composite motor cases undergo shrinkage on polymerization. This shrinkage causes an inherent defect due to the stress which develops in the manufacture of the motor case.
The modified epoxy resin blend disclosed in U.S. Pat. No. 4,515,912 is comprised of a first component mixture of diglycidyl ether of bisphenol A (EPON 828) 50 parts and epoxidized Dimer acid (EPON 871) 50 parts; a second component of butanediol diglycidyl ether 25 parts; and a three component mixture of TONOX 60/40 (20 parts) which is comprised of 65% 4,4'-diaminodiphenylmethane, 10% triamines, and 25% polyamines. The TONOX 60/40 (20 parts) is replaced with 20 parts of a third component of the curative o-phenylenediamine-boron trifluoride etherate, and to the above parts of ingredients excluding TONOX 60/40 is added about 15 parts of a fourth component of the bisspiroorthocarbonate, 3,9-bis(5'-norbornene-2'yl)-1,5,7,11-tetraoxaspiro [5.5]undecane. The modified resin is a resin which expands during curing rather than shrinks during curing whereby the inherent stress normally formed from shrinkage during curing is elimiated or substantially reduced.
The technology of expandable adhesives has been one of major interest because these adhesives produce bonds from an adhesive matrix that are substantially void-free and stress-free.
Applicant's U.S. Pat. No. 4,574,132, filed Nov. 9, 1984, discloses the general purpose expandable adhesive comprised of a spiroortho ester synthesized from the lactone, 6-caprolactone, and the diglycidyl ethers of bisphenol A and 1,4-butanediol, Cab-o-Sil, silica (325 mesh) thickener/thixotrope, and Unirez 2800, amidoamino curing agent, has superior tensile strength, superior bondability and with less void formation to aluminum, steel, wood, and cured concrete as compared with a general purpose adhesive which does not contain a spiroortho ester.
For tailoring the optimum shrink characteristics of a copolymerized product of a compound selected from 6-hesanolactone and 5-norborne-2,2-dimethanol with a compound having an oxiranyl (epoxy) group, it is desirable to produce a laminate in which the reinforcing fibers will not undergo breakage, or pull out of the matrix.
Therefore, an object of this invention is to provide a product wherein a predetermined amount of the reaction product of a compound selected from 6-hexanolactone and 5-norbornene-2,2-dimethanol and an epoxy compound is cured with a predetermined amount of a curing agent to achieve optimum shrink resistance in the modified epoxy resin employed in the fabrication of composite, structural laminates, such as: interceptor motor cases, propellant binders, aerospace structures, prestressed precision castings, high strength adhesives, potting compounds, etc.